Constructing exterior wall structures made of stone material of buildings without a ventilation gap, the so-called ventilation slot, has been the industry custom for decades, at least in the Nordic countries. Exterior structures of stone material are masonry, plastered and other exterior wall structures, which include stony material. Because of the missing ventilation slot, such a structure is particularly sensitive to damage due to moisture. Then, the wall itself and its insulating layer can be permanently damp, which causes various health hazards. Microbes thriving in moisture, such as e.g. mould fungi, weather the walls, spread in the building and cause symptoms of diseases and a risk of losing health for people on the premises.
When repairing the stony exterior wall structures of such buildings, exterior wall cladding is traditionally pulled down first, thermal insulations are removed and new thermal insulations are installed. After this, the external cladding is re-built. Then, it is important that plinths are widened such that a working ventilation slot is provided in the structure. Such repair is sluggish and takes a long time. Furthermore, the costs of repair are high and, even when repaired, the structures do not prevent the weathering of the stony external claddings.